Teachin g Notes

Operationa l Reacto r Safet y Course

Lecture : 1 2 – Safet y Goal s a n d Ris k Inform e d Decisio n Making

Objective :

To gain an appreciation of how the regulator uses risk assessm ents in decision m a king. The sign if ic ance of c r ite r ia f o r acc e p tance of design changes base d on risk assessm ents, determ inatio n process, d ef ense in de pth, tr eatm ent of uncertainties and PRA quality are addressed. Reviews past safety goal descri ptions to be sure students understand the concepts.

Ke y Point s t o Brin g Out:

Slid e num be r Point s

3-13 Review of past lecture on safe ty goals, subsidiary safety goals and acceptan ce guidelin es for core dam age frequen cy.

Review NRC safety goals and base s of subsidiary quantitative safety goals. A good summary of quantitative safety goals as applied to th e three leve ls of PRAs. Don' t forget to include uncertainties as a factor. Us ing the United Kingdom' s risk tolerance cu rve, the US evoluti on of the use of PRA in decision m a king should be explained. Slide 11 shows how the current Comm ission is applying risk in regulation for design changes.

14 Key point on this slide is how NRC interprets defense in depth which is a corner stone of NRC safe ty philosophy. If one is designing new reactors, these prin cip l es need to b e address e d.

15-16 This slide is an im portant slide for the future applicability of risk m e thodology. Uncertainties need to be identified and addressed in all PSA analysis.

17-18 Review sign ificance determ inati on process as a m echanism to identify how risk is used to focus regulatory resources on key safety issues for enforcem ent.

19 A key area for the future of PSAs is to standardize PSA quality. NRC has commissioned several standards by ASME and ANS to develop app r oaches f o r achieving q u ality such that the r e is confidence in the resu lts in the use of PSA.

20 A good summ ary slide of NRC' s approach to a risk inform ed regulatory system .

21 This safety monitor slide should introduce how util ities are using risk m e trics in operations. Go over what the key indicators are including C D F and LERF as well as the safety targets. Explain utilities use of risk in m a intenance and outage planning.

MIT OpenCourseWare http://ocw.mit.edu

22.091 / 22.903 Nuclear Reactor Safety

Spring 200 8

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